The Command Center was the Secret Service, and their mission was clearly not to inconvenience the young lad.
The assassin figured out the right spot for his killshot. The FBI/Schutzstaffel/local police thought it was just too difficult to position someone there. Scorecard: Assassin 1, Public Security 0, We DO have such deep thinkers at the FBI and Schutstaffel, don’t we?